Modern lubricating oils used in internal combustion engines contain dispersants. These prevent the accumulation of engine sludge. However, such dispersants are surface active agents, and it has been found that their use can lead to a phenomenon called "emulsion-sludge". This occurs in overhead valve engines including overhead cam engines on the engine parts under the rocker cover. Water can accumulate in this zone especially in cold weather and combine with engine oil to form a water-oil emulsion having the consistency of mayonnaise.